Communication system



Nov. 3, 1942. l. E. COLE ET AL COMMUNICATION SYSTEM Filed Aug. 51, 1940 6 Sheets-Sheet l E. COLE INVENTORS: A. E. MELHOSE WM TUTH/LL A T TQPNEV Nov. 3, 1942. E. COLE ET AL COMMUNICATION SYSTEM Filed Aug. :51, 1940 6 Sheets-Sheet 2 ATTORNEY Nov. 3, 1942.

LjEfCOLE ET 2,300,775

COMMUNICATION SYSTEM Filed Au 31, 1940 e Sheets-Sheet z 1J5 COLE lNl/ENTORS: A. E. MEL HOSE m m TUZ'l-I/LL )4 7' TORNE v Nov. 3, 1942. l. E. COLE EI'AL COMMUNiCATION SYSTEM Fil ed Aug. 51, 1940 6 Sheets-Sheet 4 IE. COLE INVENTORSEA. E. MELHOSE ATTORNEY Nov. 3, 1942. 1. E. COLE ET AL 2,300,775

COMMUNICATION SYSTEM Filed Aug. 31, 1940 6 Sheets-8 116915 STRONG JIGNA L S WAK SIGNALS 1.5. COLE lNl/EN TORSz/if, MEL HOSE y 7 m n: rum/1.1.

Patented Nov. 3, 1942 COMIMUNICATION SYSTEM Ira E. 001e,.Montclair, and Alfred E. Melhose, Westfield, N. J., and Walter W. Tuthill, Jackson Heights, N. Y., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application August .31, 1940, Serial No. 354,920

11 Claims.

This invention relates to communication systems and particularly to interpolated telegraph and speech systems wherein telegraph signals are interpolated in telephone conversations during lulls and pauses therein.

Where communication channels including suitable links are employed and where telegraph signals are transmitted in the form of voicefrequency alternating currents a telegraph signal receiver known as a telegrad is employed. This device as fully disclosed in Patent 2,238,028, granted April 15, 1941, upon the application of Barney et al. has the characteristic of effectively delaying the telegraph signals passing therethrough. A filter network having low attenua tion to telegraph signal frequencies but high loss to all other currents is essentially a part of the telegraph receiving circuit and is included in the term telegrad. It is in this band-pass filter that the greater. part of the time in transmission is st.

Where the circuit into which the telegrad relays the telegraph signals must be controlled by the circuit over which the telegrad receives the signals, such control must be exercised in proper time relation to the flow of such signals. Therefore, a time delay comparable to the time delay caused by the telegrad must be introduced in the said control circuits.

In the specific embodiment of the present invention herein disclosed by way of example, the telegraph signals, delayed in passing through the telegrad, operate a printer. This, printer has a separate control, the circuit for which must be kept closed to insure continuous operation. Particularly this circuit must be kept closed to insure-theprinting operation at the end of the selecting operation responsive to the signals from the telegrad. If this circuit is opened during the selecting operation, then the character being set up will not be printed and'will be lost if not retransmitted.

The means for operating this separate control of the printer is a relay means operated from the transmission channel and not'subject to the delay to which the telegrad subjects the telegraph signals. Therefore, it becomes important to prevent premature disabling of this separate printer control when the complete series of telegraph signals have been delivered to the telegrad but due to the delay have not been completely delivered by the telegrad to the printer, for such complete series of signals will be properly delivered and the printer should be allowed to completeits printing function.v Since the complete series has been delivered to the telegrad, the transmitting apparatus at the distant transmitting end will step to the next character and hence, if the printer at the receiving end is prevented from printing, such character will be lost and it will then be said that the telegraph message is mutilated. l The object of the present invention is to render switching operations'in circuits including delaying telegraph relay circuits more accurate. This is of particular importance inthe interpolated telegraph and speech system wherein the.

telegraph transmission must be interrupted employed to insure the complete transmission of the code and hence the complete reception of the code must be insured, otherwise the message as printed may be mutilated.

A feature of the invention is a hang-over circuit for the control means operating the receiving circuit fed by the telegrad. By this means such control means, which is controlled. simul taneously with the input of the te1egrad, is

caused to operate simultaneously with the out put of the telegrad.

Another feature of the invention is a fast operating slow releasing relay for controlling the switching operations of a circuit operated by a I telegrad. V I

Still another feature is a means for insuring the complete printing operation of a printer when the complete series of signals for a char.

acter have been delivered to a delaying telegraph signal relay.

The drawings consist of six. sheets containing Figs. 1 to 9, inclusive. Figs. 1 to 4, when placed together as indicated in Fig. 5, show a circuit diagram partly schematic, of one terminal of .an interpolated telephone and telegraph system.

Fig. 1 shows the transmitting telegraph circuits; V

.Fig. 2, partly schematic andpartly circuitdiashows the telephone and controlling circuits;

Fig. 3 shows the receiving telegraph circuits;

4 is a detailed circuit diagram of the major portion of the telegrad, a telegraph gain regulating amplifier detector;

Fig. 5 on the same sheet with Fig. 1 shows how Figs. 1, 2, 3 and 4 are to be placed;

Fig. 6 is a detailed circuit arrangement of the control tone compressor indicated by the rectangle 242 in Fig. 2 and fitted into'the' general diagram of Fig. 2 at the broken lines X-X, Y-Y and ZZ;

Figs. '1 and 8 are explanatory diagrams illustrating the transition of a signal in the telegrad from an alternating current varying strength signal to a direct current uniform strength signal.

These diagrams particularly show the displace ment in time between the input and output signals. Fig. '1 shows a strong input signal and Fig. 8 shows a weak input signal; and

Fig. 9 is another explanatory diagram showing the timing relation of the switching means employed in the present invention.

One terminal of a system is shown but it will be understood that at some distant point a similar terminal is located so that speech coming in over channel 20! will be transmitted from the radio transmitter 202"and its antenna 203 to be received at the said distant point over the antenna 204 and the radio receiver 205 for transmission into the speech path at that point corresponding to the channel 20 I.

While speech is being transmitted from channel 20I over the antenna 203, the telegraph transmitting apparatus of Fig. 1 is inactive and the telegraph receiving apparatus of Fig. 3 at the distant point is similarly inactive. By the same token the telegraph transmitting apparatus of Fig. 1 at the distant point and the telegraph receiving apparatus of Fig. 3 at the near end, as shown, will be in operation.

In general, speech over channel 20I enters the hybrid coil 206 provided with the usual balancing network 201, passesover path 203 through the network 209 to the voice operated gain adjusting device (termed vogad for short) 21 I. From the vogad 2 speech currents enter the hybrid coil2I2 where they split, part going on to the main speech channel and part entering the syllabic amplifier-detector 2I3 for control purposes. The output of the amplifier-detector 2I3 feeds into the transmitting chain 254 which performs a variety of switching functions, as will be more clearly set forth hereinafter. At present it is sufficient to say that the transmitting chain 2 I4 clears the Way for the speech currents to the antenna 203 and that the distant receiving terminal similarly conditions the receiving circuits thereat for the proper reception of the speech currents. The main portion of the speech currents then pass from the hybrid coil 2I2 into the delay circuit 2H5, through a repeater 2 I5, and the first transmitting suppressor 2I1. Thereafter the speech path is through privacy circuit 2 I 8, the second transmitting suppressor M9, and another part of the privacy circuit 220 to the hybrid coil 22 I. Speech currents then pass to the hybrid coil 222, thence to the transmitting repeater 223 to the radio transmitter 222.

At the distant receiving end the speech currents transmitted from the radio receiver pass through the receiving repeater 224 into the hybrid coil 225. At this point the control tone which accompanies speech is diverted to the control tone filter 226, to the receiving detector 221, which operates the receiving chain 228. This receiving chain responds to the control tone transmitted from the distant end through the operation of the transmitting chain 2M thereat and like the transmitting chain performs a variety of switching functions which will be more fully described hereinafter. At present it is sufficient to say that the receiving chain clears the way for the speech currents to reach the hybrid coil 206 and channel 20f. The speech currents leaving the hybrid coil 225 enter the next hybrid coil 229 and thence pass through a part of the privacy circuit 230,

the first receiving suppressor 23l, another part of the privacy circuit 232 to the second receiving suppressor 233. From this point the speech currents pass through the variable suppressor 234, a low-pass filter 235, a volume controller 238, a repeater 231, a network 238, and thence to the hybrid coil 206 from which they pass over the channel such as 20I at the said distant terminal.

The functions of these various pieces of appa ratus are briefly as follows.

Referring to the details of the speech control circuits, the hybrid coil 206 receives voice currents from the channel 20I and transmits them out over the channel 208. The hybrid coil 206 also receives voice currents from channel 239 and transmits them out over channel 20I. Actually the voice currents split equally to paths 208 and 239 but are prevented from passing over 239 beyond the repeater 231 by the unidirectional characteristics of this repeater. The function of the balancing network 201 is well known. In this connection it should also be noted that each of thehybrid coils 2I2', 22I, 222, 225 and 229 are provided with appropriate balancing networks. The networks 200 and 238 are provided to perform certain functions necessary in commercial telephone circuits to compensate for the differences in transmission when the channel MI is connected to different types of telephone circuits. Their adjusting circuits are not shown but theyare included in the schematic part of'this diagram in order to render the diagram as complete as possible. The vogad 2H is a means for adjusting the gain applied to the voice currents incoming thereto so as to provide a uniform level of output. The hybrid coil 2I2 allows a small part of the voice currents to be taken off to the syllabi'c amplifier-detector 2I3 without causing distortion in the voice currents fiowing from the hybrid coil 212 to the rest of the circuit. The delay circuit 2I5 is an arrangement by which voice currents are delayed to allow time for the transmitting chain 2 to properly perform its functions before the voice-currents are finally delivered to the antenna 203. Since these delay circuits entail a certain loss in transmission, amplifying means are associated therewith in the form of a repeater 2I6 which is shown as a oneway amplifying repeater. The first transmitting suppressor 2H and the second transmitting suppressor 219 both act to block speech currents therethrough when the relays of the transmitting chain 2M are in the position shown. When, however, the transmitting chain is operated both transmitting suppressor H1 and transmitting suppressor 2I0 give a clear path for the transmission of voice currents. It is necessary to use a blocking path at each terminal of the privacy system circuit 2 I 8, this being a controlling agency for the other part of the privacy system 220. These two units 2 I8 and 220 are included to render the speech between the antenna 203 and the distant antenna 204 unintelligible but do not form any essential part of the present invention being included again for the purpose of rendering the schematic layout as complete as possible. The function of the hybrid coil 2'2l is to transmit to the hybrid coil 222 either speech coming from the privacy system unit 220 or telegraph signals coming from Fig. 1 above. The function of the hybrid coil 222 is topass on to the transmitting repeater 223 both the output of the hybrid coil 22! and the control tone originating from the oscillator 240. This oscillator is a source of alternating current of a frequency just outside the voice range so that it may be efiectually filtered out at the receiving end without disturbing the voice currents entering the receiving circuit thereat.

Current from the oscillator 240 enters the control tone enabler 24l, which is under control of the transmitting chain 2| 4, as will appear hereinafter. When the voice takes command of the transmitting chain M4 and certain'relays in the telegraph transmitting apparatus of Fig. 1 are properly operated, the control tone enabler 24L voice takes command of the transmitting chain 214, control tone at full volume will be delivered to the hybrid coil 222. A short time thereafter, as measured by the delay circuit 215 and controlled by a connection in the voice path between the first transmitting suppressor 2|! and the first unit of the privacy system 2l8, the control tone compressor will operate to reduce the volume of the control tone being delivered to the hybrid coil 222.

The transmitting repeater 223 is a well-known type of one-way amplifier. The radio transmitter 202 and its associated antenna 203 need no special description. Likewise, the radio receiver 205 and its associated antenna 204 need no special description. The repeater 224 is, l ke the repeaters 2 l6 and 223, a one-way amplifying device. The hybrid coil 225 receives the output of the radio receiver 205 and allows part of this output to flow to the control tone filter 226 which delivers to the receiving detector 22! only the control tone. 7

The hybrid coil 225 also delivers-to the next hybrid coil 229 the speech currents, the accompanying control tone being filtered out later. Hybrid c-oil 229 acts during the transmission of speech currents to deliver the speech currents which are transmitted from the radio receiver 205 to the privacy system unit 230 and the various circuit units thereafter. During intervals of telegraph transmission the hybrid coil 229 delivers the output of the radio receiver 205 to the telegraph receiving apparatus of Fig. 3.

The privacy system units 230 and. 232, like the privacy system units 220 and 2l8, are used to insure secrecy in the transmission of intelligence by translating for delivery tochannel '20! the otherwise unintelligible transmission from the antenna 203 to the antenna 204. The first receiving suppressor 2'31 and the second receiving suppressor 233, which both operate under control of the receiving chain 228, operate to block the speech path during those intervals when the control tone is absent from the transmission being received by the receiver 205. When control tone is present as an indication that speech is present, the receiving chain 228 is operated and the receiving suppressors 23l and 233 give a clear path for speech currents toward the hybrid coil 206 and the channel 20l. The variable suppressor 234 is a device used to cause the transition from speech to silence and from silence to speech to 2 be slow so that clicks and unpleasant operation of the circuit will not disturb the listener. The lowpass filter 235 effectually blocks any control tone which may have accompanied speech to this point and allows only the speech to go into the volume controller 236.

At this point it should be noted that between the low-pass filter 235 and the volume controller 236 there is a connection to the receiving detector 221. Thus when the voice takes command at the distant transmitting end, control ton from the oscillator 240 is transmitted by the radio transmitter at full volume, and this will enter the control tone filter 226 and the receiving detector 22'! to insure the proper operation of the receiving master relay within the receiving chain 27.8. By the time that the voice arrives the receiving chain will have conditioned the receiving circuit, particularly by operating the first and second receiving suppressors 23! and 233 and the variable suppressor 234 so that as the control tone is reduced in volume through the action of 'the control tone compressor 242, voice currents from the connection between the low-pass filters 235 and 236 willreach the receiving detector 231 to augment the operation of this device and insure the proper and continuous operation of the receiving chain even during periods when fading or other disturbances in the mutable link cause the received control tone to drop to a value where the continued operatic-n of the receiving chain might be unsatisfactory.

The circuit diagram of Fig. 6 shows in detail the control tone compressor 242. The single lines crossing the broken lines XX, Y-Y and ZZ represent a pair of circuit conductors as indicated in Fig. 6. Thus the single line crossing the broken line Y Y represents a speech path entering the control tone compressor and connecting to the primary winding of the transformer 600. The secondary winding of this transformer connects to a potentiometer 60! having an adjustable point .602 which may be moved to'diiferent positions for adjusting the sensitivity of the device. From the potentiometer point 602 a well-known type of pentode' amplifier tube 603 is controlled. The plate circuit of this tube feeds into an interstage transformer 604 which in turn feeds the amplifier speech currents into a double diode triode tube 605. The diode portion of this tube acts as a rectifier and the triode portion acts as an amplifier. Thus the speech currents entering the transformer 600 are transformed into a varying strength direct current corresponding to the strength of the speech currents. The plate'circuit of the tube 605' may be traced from batteryv 606 and thence through'two parallel paths in the.

varistor 601 to the plate of tube 605. The varistor 601 is a variable loss device the loss value of which is controlled by the direct current flowing in the plate circuit of tube 605.

The line crossing the'broken line X--X represents a circuit from the control tone enabler 2 and the line crossing the broken line ZZ represents a path leading into the control tone filter 243. The control tone, thereforeyenters the primary of a transformer 608, passes through the varistor 60! and enter the transformer; 609,

which feeds into the control tone filter 243. Under the condition where no speech currents are entering th transformer 600 the loss of the varistor 601 is low, the alternating current from th source 240 passing easily through the copper oxide rectifiers 6I0 and (H I. When the volume of speech entering the transformer 600 is low, the current flow in the plate circuit of tube 505 affects the copper oxide rectifiers Em and 6 so as to introduc a certain amount of loss in the control tone path. Speech of greater volume will correspondingly introduce greater loss in this circuit. Hence the amount of control tone passing through the varistor B01 is a function of the amplitude of the speech currents entering the transformer 600.

Generally speaking, a device of this nature is employed so that the total load on the radio transmitter 202 remains practically the same, that is, the transmission of voice currents and control tone should approximately add up to the same algebraic sum at all times. The effect at the receiving end is that the combined output of the detector 22'! is practically uniform whether it comes from the control tone source alone or from the combined contro1 tone and speech current provided in the manner hereinbefore described.

That part of the circuit between and including radio transmitter 2532 and radio receiver 205 is spoken of as a mutable link since it comprises a signaling channel capable of or liable to change from internal or external cause which may give rise to interfering energy or more specifically, subject to noise, fading or change of attenuation. It is to be understood, however, that the present showing is by way of example and that the term mutable link does not necessarily mean that a space radio link is necessarily involved but that the term is broader in its meaning and includes any channel liable to change from internal or external cause.

The volume controller 236 is a device generally under the supervision of a technical operator for controlling the volume as indicated by a monitoring device, not shown, connected between this unit and the receiving repeater 23?. The receiving repeater 231 is like the other repeaters 2I6, 223 and 224, a one-way amplifying device.

The syllabic amplifier-detector 2E3 is a device which will be unoperated by the maximum noise which may be expected on th transmitting circuit but will be operated quickly by speech signals of both high and low amplitudes. It is connected to the hybrid coil 2G2 and delivers its output. to the receiving chain 2 I 4.

The transmitting chain 2I4 has control over a number of pieces of apparatus. For instance, the lines leaving the transmitting relay chain 2 I4 and ending in arrow-heads before the transmitting suppressors 2I'I and 2H! indicate control over these suppressors by the transmitting chain. Likewise, the transmitting chain has control over the privacy circuit unit 2I8. Another line extending from th transmitting relay chain 2M passes through the armature and back contact of relay I04 in the telegraph transmitting apparatus and ends in an arrow-head at the control tone enabler 24I, indicating that the transmitting relay chain controls said control tone enabler at all times when th relay I04 is in its normal position. As will be explained hereinafter, relay I04 operates at a particular time in order to delay the control of the contro1 tone enabler by the transmitting relay chain. .An-

other control from the transmitting relay chain 214 passes through th 'back contact and armature of relay I00, the resistance IOI and the windings of relays I02 and I03 to battery. When the transmitting relay chain operates this latter circuit is closed and disables the telegraph transmitting apparatus.

In like manner the receiving relay chain 228 controls the first receiving suppressor 23I, the second receiving suppressor 233 and variable suppressor 234. Another control extends from the receivin relay chain 228 to the syllabic ampliher-detector 2I3 and will disable this amplifierdetector when the said: receiving relay chain 228 is operated. A further control extends to the vogad 2 which acts for the purpose of maintaining the gain of this device at the point last set.

A relay 214 is indicated as being one of the relays of the receiving chain. This relay controls a normal open circuit extending to conductors 402 and 493 in the telegrad. The purpose of this will be explained more fully hereinafter.

The transmitting telegraph apparatus consists, generally, of a pair of tape transmitters I05 and I85. Each of these transmitters has a series of five contacts operating between a spacing battery lead I01 and a marking battery lead I08 and affecting, in turn, the segments III to I20, inclusive, of the multiplex distributor. This latter piece of apparatus consists, in general, of a motor and synchronizing equipment IIO operating a shaft I09. This shaft has uponit a number of brushe I2I, I22, I23 and I24. The brush I2I as it passes successively over the segments III to :20, inclusive, connects these segments to the ring I25 which is connected through either the armature and back contact of relay I26 or the armature and back contact of relay I21, thence through the back contact and armature of relay I03 and the winding of the telegraph transmitting line relay I28 to a point on a potentiometer consisting of the resistances I29 and I30 whereby the relay I28 will respond to either marking or spacing potential and thus operate its armature accordingly. When relay I28 is operated by a spacing signal it closes a circuit through its armature and contact to render the telegraph tone enabler I3! ineffective to transmit telegraph tone from the source I32 to the hybrid coil 22 I. When the relay I28 is operated by a marking signal it opens this circuit which affects the telegraph tone enabler I3I in such a way that alternating current from the source I32 freely passes to the hybrid coil 22I and thence out over the radio transmitter 202.

It should be noted that when the transmitting chain 2 I4 is operated and, consequently, relay I03 is operated, that a connection is extended from spacing battery lead I01 through the front contact and armature of relay I03 to the winding of relay I28 to hold this relay spacing and, therefore, continuously to block the transmission of telegraph tone from the source I32 to the hybrid coil 22I.

The function of brush I22 is as follows: If the transmitting chain operates at any time before brush I22 comes in contact with segment I33 or segment I34, then relays I02 and I03 will be properly operated and further transmission of telegraph signals interrupted and the stepping of the tape magnet prevented. If, however, the operation of the transmitting chain 2I4 occurs whil brush I22 is on either of these segments I33 or I34, aconnectionwillbe extended from. battery, ring I35 over brush I22 to segment I33 and thence through the windings of relays I04 and I00, and the back contact and armature of relay I02 to ground. This causes the circuit for the operation of relays I02 and I03 to be opened to prevent the disabling of the telegraph apparatus for this very short interval. This arrangement is provided so that if the voice takes command of the circuit at or during the transmission of the last pulse of a telegraph code, this last pulse may be allowed to be transmitted without interruption,'and the operation of the tape stepping magnet insured.

The function of brush I23 is as follows: The segments and rings of this multiplex distributor are developed for the sake of clarity and the brush I23, now moving downwardly, has reached the point where transmission of the signals from the tape transmitter I06 has been completed. Brush I23 now establishes a connection from ground, ring I35,brush I23, segment I31, back contact and outer right-hand armature of relay I38, winding of stepping magnet I39, right-hand contact and armature of relay, I40 to battery. If relay I 43 is on its right-hand contact, as it should be while this apparatus is operating normally, and there is a sufficient supply of tape for use by the transmitter I06, then the magnet I39 will operate and advance the tape to the next punched character. As brush I23 advances it next comes into contact with segment I4I where a connection is established from ground, ring I38, brush I23, segment I4I, the contacts of the taut tape switch I42, which will be closed as long as there is sufiicienttape in this transmitter, to the lefthand winding of relay I38. This connection also extends in parallel through the normal contacts and the inner right-hand armature of relay I38 through the right-hand winding of .this relay, and these windings being opposed no operation of the relay I38 will occur. If, however, upon the operation of magnet I39 the taut tape switch I42 had operated, then only the right-hand winding of relay I38 would have been energized and this relay would then have operated and looked through its inner right-hand armature to ground. This condition would have persisted until the taut tape switch I42 closed its contacts again and brush I23 made contact with segment I4I whereupon the relay I38 would. have been automatically released.

During the time that relay I38 is operated each of the segments I I6 to I20, inclusive, would have been connected through the front contacts and left-hand armatures of relay I38 to marking battery, so'that a signal consisting of five marking pulses would have been repeatedly sent each time the brush I 25 passed over the segments IIB to I20, inclusive.

When brush I23 advances to segment I43 2. connection is momentarily established from ground, ring I38, brush I23, segment I43, the lower winding of relay. I40 to battery. Thistends to drive relay I40 to its right-hand contact where it will remain unless some other circuit is closed to change this condition. I

As brush I23 advances further it first causes the. operation of stepping magnet I44v in a simi- I39 and attempts to operate the relay I45 and finally closes a circuit to driverelay I46 to its right-hand armature.

The function of brush I24 is asfollows: If durrelay I02'becomes operated, then a circuit will be established from ground, the armature and front contact of relay I02, ring I48, brush I24, segment I41, the upper winding of relay I46 to battery. Relay I46 will thereupon be driven to its left-hand contact where it will remain until brush I23 drives it back to its right-handcontact. During the time that relay I46 is on its left-hand contact it will cause the operation of relay I26 in an obvious circuit and thereby open the transmitting circuit which operates the telegraph transmitting relay I28. When brush I24 reaches, the lower segment I49, it will cause the relay I40 to move to its left-hand contact whereupon the relay I21 will be operated and complete the opening of the circuit for relay I28. It will be noted that each of these relays I46 and I40 will be periodically returned to its right-hand contact at the ending of the period of activity of the other circuit, but if the telegraph transmitting apparatus is now rendered ineffective, the, relay will return to its left-hand contact immediately thereafter and before any signals can be effectively transmitted.

It should be noted before leaving the description of the transmitting telegraph apparatus that if both the taut tape switches open the left-hand windings of relays I38 and I45, respectively, that the contacts and the left-hand armatures of relar manner to the operation of stepping magnet ing the time thatbrush I24 is on segment I41,

lay I45 are connected to spacing battery so that first a series of five marking impulses and later a series of five spacing impulses will be transmitted. This provides for an occasional transition between a spacing and a marking impulse for the purpose of correcting the distributor speed at the distant end.

' When the receiving chain 228 is in its normal unoperated condition then the telegrad will be enabled. This will render the telegrad effective to operate the receiving telegraph apparatus. At this time telegraph signals being received by the radio receiver are passed into hybrid coil 229 and thence into the band-pass filter 30I (which is essentially a part of the circuit generally termed telegrad) from which they are delivered to the telegrad. This results in the operation of relays 302, 303 and 304 to their marking contacts f r each marking impulse delivered to the telegrad.

The device known as the telegrad is shown mostly on Fig.- 4 and partly on Fig. 3. The telegraph signals leaving the hybrid coil 229 enter the band-pass filter 3M and pass through the circuit of the telegrad eventually appearing as direct current signals entering the upper windings of relays 302, 303 and 304 in series. Each marking signal will operate these three relays to their left-hand contacts and each spacing signal will operate these three relays to their righthand contacts.

Signals coming from the band-pass filter 30I pass through a vario-repeater consisting of two stages, first, a copper oxide vario-losser pad and secondly, a push-pull variable-mu amplifier stage. The signals passthrough a transformer 40I and thence through a cross-coil controller comprising a circuit including the windings of transformer 400 and transformer 40I. When the pair of wires 402 and 403 leading to the armature and contact of the telegrad disabled relay 214 are connected together by this relay no signals will pass from the band-pass filter am into the further stages of the telegrad. Inv other words, the signals will be blocked by connection of conductor 402 to conductor 403. When the receiving chain 228 is released and relay 214 returns to its normal condition, the connection between conductors 402 and 403 will be opened and signals Will pass freely into the circuit beyond transformer 40l.

At this time the signals pass through the copper oxide vario-losser pad to transformer 404. From transformer 404 they pass in push-pull relation through two variable-mu suppressor pentode tubes 405 and 406 to another transformer 401. The copper oxide vario-losser pad comprises four copper oxide rectifiers 408, 409, M and 4H connectedin a bridge circuit across the outer terminals of transformers M2 and 404 with a pure resistance 4l3 bridged thereacross. The outer apex points of this bridge are connected in one case to a potentiometer 4I'4 between plus battery and ground and in the other case to the mid-point of the primary winding of transformer 401. The current flowing in the copper oxide bridge is then a function of the plate curflowing through resistance M5 the smaller will be the direct current flowing through the copper oxide bridge.

The important element in this vario-repeater is a condenser M6. The potential of the upper plate of this condenser determines the gain to the signal. The gain of the vario-repeater is increased by the raising of the positive charge on condenser M6 and is reduced by a corresponding reverse action adjustment. Through the use of a potentiometer 4|! the potential of the upper plate of condenser MS may be kept at such a point during idle periods that the Vario-repeater is set at mid-gain.

The signals going out from transformer 40'! pass through a suppressor grid pentode tube M8 and thence to a hybrid coil comprising the circuit connected between transformer M9 and transformer 420. The output of this hybrid coil works into a suppressor grid pentode tube 42!, acting as an amplifier, to a transformer- 422 and thence to a full wave rectifier tube 423. Under normal conditions, that is, in the condition of a spacing signal, a suppressor grid pentode tube 424 is so adjusted by the potential of the midpoint of the secondary of transformer 422 that 4;

current flows from the plate of tube 424 through a neutral relay 350 and the lower winding of relay l holding them in the positions shown.

When a marking signal is transmitted then a direct current voltage is produced across the diode resistance 425 and the negative voltage reduces the plate current from tube 424 to a point where relay 350 releases and the biasing current in the upper winding of relay 35l drives this relay to its marking contact. When relay 35I moves from its spacing contact, a short circuit on the hang-over condenser 355 is removed and this condenser in time is charged by the positive battery connected through the lower winding of relay 352. This charging current holds relay 352 on its spacing contact for the hang-over period. Thereafter as the biasing current through the upper winding of relay 352 becomes effective and relay 352 moves to its marking contact, a circuit is closed from ground through the armature of relay 351 and its marking contact, thence through the armature of relay 352 and its marking contact to the receiving relays 302, 303 and 304.

Since the telegrad is used at the output of a selective filter 30l, the length of the pulses reaching the input is longer than the signal transmitted. Since relay 35l follows the signals at the input of the telegrad, the circuit including relay 35! and the hang-over condenser 355 is provided to regulate the length of the pulses going out to the receiving relays 302 to 304, inclusive, to the length of the pulses before they pass through the band-pass filter 30 I.

In general terms, then, alternating current impulses which may vary from strong signals to very weak signals over a range of some 45 decibels are converted by the vario-repeater into alternating current signals of a practically uniform amplitude. These signals then pass through an amplifier-detector and appear at the output of the tube 424 as direct current signals and later in the upper windings of relays 302 to 304, inclusive, as direct current signals of uniform strength and of a length equal to the signals delivered to the band-pass filter 30L It was pointed out above that the potential of the condenser M6 is normally adjusted by the potentiometer 411 to a point where the variorepeater is set at mid-gain. If a very weak signal is received a gain increaser circuit operates to bring up the gain of the vario-repeater in a very short time. This time, for example, may be a minor fraction of a signal length. For a further specific example, this period may be of the order of 5 to 6 milliseconds, so that where the signal length is of the order of 22 milliseconds the time taken to change the gain of the variorepeater becomes a minor fraction of the signal length.

The signaling current then passes into a transformer 426 through an amplifier comprising essentially a suppressor grid pentode tube 421 to a variable loss device comprising the circuit between the transformers 428 and 429. When relay 350 is in the position shown, the variable loss device 430 is in such condition that the alternating current signal will manifest itself in transformer 43! and thus place an alternating current potential at the terminal of the cold cathode gas-filled tube 432. This breaks down the gas tube and current flow therethrough is started, current flowing from a point on potentiometer 433 connected to plus battery through the tube 432, resistance 434 to ground. The drop across resistance 434 causes a second cold cathode gas-filled tube 435 to break down and thus apply positive potential to the condenser 4I6. Since the impedance of this condenser charging circuit is very low the condenser 4| 6 is charged rapidly and the gain is changed, for example, in the order of 20 decibels in approximately 5 milliseconds.

When the gain has been brought up to the point where a direct current signal is produced by the tube 434, manifesting itself through the release of relay 350 and the movement of relay 35l from its spacing to its marking contact, this gain increasing circuit is disabled.

The disabling is done in two steps; first, the armature of relay 350 moves from its front contact and thus opens the circuit of the variable loss device 430 so that this circuit now becomes opaque to alternating current and the alternating current ceases to flow in the transformer 43L Thus the circuit for activating the tube 432 is disabled. Secondly, and shortly thereafter when the armature of relay 350 reaches its back contact, a ground is placed on the lower side of the secondary winding of transformer 43! or, in other words, on the potentiometer point supplying positive potential to the tube 432 so that the enabling voltage normally applied to this cold cathode tube is reduced to ground potential.

Heretofore the gain increase disabler of circuits, known as vogads, have been operated di-' rectly by relay contacts. An analogy would be the charging circuit for condenser 4|6 passing through the contacts of relay 350. The transient voltage of this circuit, however, on opening the charging circuit is so high that the relay contacts cannot be used alone, and hence the gain increaser is disabled in the two-step manner just described, consisting of first disabling the activating circuit, and secondin disabling the operat ing circuit of the gain increaser.

In order to keep the potential of the control condenser 4 l 6 from going too high when the gain increaser operates, the condenser M6 is shunted by a rectifier 438. condenser M6 to a predetermined maximum value.

Two leads coming from the lower part of the hybrid coil comprising the circuit between the transformers M9 and 420 lead to a transformer 436 to apply voltage to the control gap of a gas tube 431. This breaks down the tube and causes the control condenser 4| 6 to be charged negatively. This circuit constitutes a fast-operate backward-acting gain decreaser. for example, will reduce the gain by decibels in a period of 4 milliseconds.

Generally the action of the telegracl is as follows. When. a weak signal is received, the gain increaser circuit causes the cold cathode tubes 432 and 435 to close the circuit for the charging of condenser 416 from a source of positive potential which acts to rectify the alternatin current of the signal transmitted through the tube. 421;

As the level of the signal at the transformer 420 reaches a predetermined point, relay 350 will be released and .the gain decreaser circuit will come into operation. Due to certain electrical delays and the mechanical delay in the armature-travel time of relay 350 to gain increaser is not disabled until the gain has gone slightly above the desired point. The gain decreaser then adjusts the signal with the result that a characteristically enlarged head is given to the intermediate stage signal, that is, the signal as it passes into the transformer 420.

When a strong signal is received the gain decreaser and the gain increase disabler relay operate at once subject to the inherent electrical and mechanical delays in the circuit and the gain increaser is disabled almost immediately again with the result that the intermediate stage signal appears to have a characteristically enlarged head.

By increasing the speed of the charging cir cuits of the condenser M6 the enlarged head will be made more prominent and by decreasing such speed the enlarged head may be reduced to a minimum.

When the gain decreaser has brought the potential of condenser 4|6 down to the proper level, tube 431 will cease to function and the charge on condenser 4l6 will remain constant thereafter except for-the slow drift to mid-gain through potentiometer 4I'I.

This is shown in Figs. 7 and -8, Fig. 7 representing a strong signal and Fig. B'representing a weak signal. These figures have been drawn from oscillograms derived from actual experience and represent the transmission of the :letter Yin This limits the voltage of the This circuit,

a well-known code. In each case there is a mark ing signal in the first, third and fifth places and a spacing signal in the second and fourth places. The upper line in each case represents the signal as it enters the band-pass filter 39!, the middle line represents the intermediate stage signal as it enters the amplifier-detector through the transformer 429 and the lower line represents the signal passing through the upper windings of relays 392 to 304, inclusive.

It will be noted that the direct current signals are displaced in time in relation to the alternating current signals from which they were derived. Thus, in Fig. '7, the vertical line 369 represents in time the starting of an alternating current signal shown in the upper line. The vertical line Hll shows the corresponding starting time of the direct current signal. The length of time between the vertical lines 199 and Hill is practically uniform without regard to the strength of the signal. Thus, in Fig. 8 the vertical line 899, for instance, marks the beginning of an alternatingcurrent signal shown in the upper line and the vertical line 99! represents the starting time of the corresponding direct current signal. It will be-noted that the distance between the lines and 'llll is practically equal to the distance between the lines 890 and 381.

In accordance with the present invention then the condenser 349 is provided and its value so adjusted that after the original energizing circuit,

for relay 339 is opened, this relay will not release for a time closely approximating the time between the lines 199 and MI or 800 and 8!.

Relay 362 is known as the receiving telegraph line relay and for each marking impulse it establishes a ground connection to the ring 385. Relay 394 is known as the corrector relay. Upon each spacing impulse this relay will cause its condenser 396 to be energized and upon each marking impulse this relay will deliver the condenser discharge into ring 391. Relay 393 is known as the auxiliary relay and operates on each marking impulse to drive either relay 308 or relay 309 to its left-hand contact, respectively.

The receiving telegraph apparatus consists, generally, of two printers 3H3 and 3! l and a mu1- tiplex distributor comprising a motor and certain synchronous equipment 3| 2 operating a shaft 3l3 carrying brushes 3M, 3l5, 3|6 and 3H.

326 and 321 to the selecting magnets of printer 3H1. Thus, for each marking impulse, one of the selecting magnets of printer 3 or printer 3H3 is operated.

Brush 316 in moving downwardly makes contact with segments 328 and then 329 whilebrush 3l4 is traversing the connections to the selecting magnets of printer 3 I. and 3 29 are associated with printer 3H3. The connection to segment 328 establishes a circuit from ground, ring 330, brush 316, segment 328, armature'and contact of relay 398 to the printing magnet 33!. Thus the selection set up on printer 3l0 is rendered effective by the printing magnet '33I after the brush 3I4 has completely traversed the segments 323 to 321 and is now engaged in passing over the segments 3%! to 322.

As the brush 3l6'advances it makes a connection from ground to segment 329, which leads to the lower right-hand set of contactsof key 332,, for purposes which will be hereinafter described.

The segments 323' As brush 3l6 nexttraverses segment 333 the printing magnet 334 will be operated.

Brush 311 makes contact from the ring 335 to the segment 336 during the time that the brush 3|4 is traversing the segments associated with the printer 3| I. This circuit from ring 335 extends a battery connection to the two windings of the relay 309 through the rectifiers 331 and 338. If this telegraph receiving apparatus is now properly in operative condition there will be an open connection to the upper winding of this relay at the armature and contact of relay 339. Any marking impulse coming in at this time will be rendered effective by the auxiliary relay 303 to keep relay 389 on its left-hand contact and thus render the printing magnet effective. If. on the other hand, the receiving chain 228 is operated by voice currents, then relay 339 will be released and ground on the armature of relay 339 will cause relay 309 to be driven to its other position where the circuit for printing magnet 334 is opened. Similar action of relay 308 will take place when the brush 3|1 traverses the segment 34| It will also be noted that when the relay 339 is operated, as when the receiving chain 228 is in its normal position, thus denoting the fact that the receiving telegraph apparatus is effective, that relay 340 will be operated. Relay 340 plays a particular role with relation to the key 332.

If the distant transmitter corresponding to transmitter I06 operates its taut tape switch so as to send out a series of five marking impulses, then the receipt of these five marking impulses by the printer 3l0 results in a thumping of the printer without the production of any printing. If this becomes annoying to the operator then the key 332 may be moved to its right-hand position. Thereupon a circuit will be established from battery, the upper right-hand contacts of key 322, the winding of relay 342, the lower right-hand contacts of key 332 to the segment 329 and when brush 316 makes contact with segment 329 a connection is extended to ground on ring 330. This causes relay 342 to operate and this relay locks up to battery on its inner right-hand armature. Relay 342 is sufiiciently slow in releasing so that it will remain locked up in a manner now to be described. Upon the first operation of relay 342 a circuit for the operation of relay 343 is closed at the front contact and outer right-hand armature of relay 342. This relaynow disconnects the segments 323 to 321, inclusive, from the selecting magnets of the printer 3|0 and extends them to conductor 344 which, with the left-hand contacts of key 332 in their normal position, extends the ground connection each time the brush 3|4 connects with a segment 323 to 321, inclusive, to the winding of relay 342 to maintain this relay operated.

If at the distant end the taut tape switch should return to normal then ground impulses willnot be supplied to the winding of relay 342at sulficient intervals to keep this relay operated and it will therefore release and by releasing cause relay 343 to return to normal, so that the printer 3H1 again becomes effective. If during the time that relay 342 is locked up the receiving telegraph apparatus is rendered ineffective by the operation of the receiving chain 228, then relay 340 returns to normal and this maintains relay 342 locked up until the telegraph apparatus is again rendered eiTective through the operation of the receiving chain-228.

' character.

The relay 342 maybe unlocked at any timeby moving the key 332 to its left-hand position.

As brush 315 movesit alternately makes contact with segments connected to either conductor 345 or 346. These conductors are connected to different windings of the corrector relay 341 and therefore the discharge of the condenser 306 will tend to operate the relay 341 in one direction if the motor 3I2 is running fast or operate the relay 341 in the other direction if the motor 3l2 is running slow. The correcting means is well known and will not be further described except to note that a device 348, which will indicate fast or slow operation, is inserted at this point to indicate that correction may be properly made.

Attention is particularly called to the condenser 349 connected in parallel with the receiving check relay 339. When the voice takes command and the receiving relay chain 228 is operated the circuit of relay 339 is opened and relay 339 releases to drive relay 308 or relay 309, as the case may be, to its right-hand position thus opening the circuit for the printing magnet 33! or the printing magnet 334. Since at the time that the receiving relay chain is operated the telegrad may not have completed the setting of the selecting magnets in printer 3|0 or printer 3| I. The operation of the relay 308 or the relay 309 would be premature if condenser 349 were not provided. When the circuit of relay 339 is opened, therefore, relay 339 will not immediately release since condenser 349 must be charged through the winding of relay 389. Thus the addition of condenser 349 provides a hang-over operation of relay 339 and this may be adjusted by the proper selection of the value of the circuit constants to equal the delay caused in the transition of a signaling impulse through the telegrad.

If relay 339 is released too soon and the character set up on the selecting magnets is therefore not completed by a printing operation, the mutilation which would result, would consist of the loss of two correctly printed characters and the substitution therefore of one incorrectly printed Such mutilation is particularly liable to occur where the telegraph transmission is interrupted near theend of the transmission of a character code or in other words when the voice at the transmitting end takes command of the channel while brush I22 is about to, or has made, contact with segment I33, for such contact insures the stepping of the tape printer and hence the corresponding action of the printing magnet 334 must also be insured.

By way of example, if the word SENT were being transmitted and the speech takes command at such a time that the transmission of the code for the letter B has been insured but due to the lack of the hang-over operation provided by the condenser 349 the printing operation is prevented by the premature opening of the circuit magnet 334. Then when the operation of the telegraph apparatus is resumed the code for the letter N will be superimposed on the code for the letter E already recorded on the selecting magnets. The code for the'lett'er E is a single marking impulse in the first code space while the code for the letter N is two marking impulses in the third and fourth code spaces. The result will be marking registration in the first, third and fourth code spaces of the selecting magnets and since this represents the code for the letter F, the printing record will appearas SFT insteadpfSENTI. Thus two correct characters are lost and are'replaced byone --incorrect icharacter.

All mutilation, of course, will not be ofthis particular character as at times the registration of the second character may not mutilate .the first or the registration of the second characterzinay not be mutilated by the first, buta-whole character will be lost. The addition of the condenser 349 prevents this type of mutilation.

The diagram. in Fig. 9' is practically. self-.ex-: planatory. It is an idealized timing chart of the terminal switching. Line 99! shows. the, .tele-.- graph signals, as manifested by the operation of relay I28, being interrupted in the. middle; of a signal. A dotted vertical line 900 represents the time at which speech shown in 1ine'902 takes command of the circuit. The next line.903 represents thetransmitting detector'and hang-over time and hence the time. duringwhichthe control tone is sent out from the source 240 is lengthened by an amount extending from the line, 9l2 representing the ending of speech to the time represented by the line 913 representing the release of the control tone enabler 24L The-line 904 represents the speech after it" has. passed through the delay circuits. The line 905 rep.

resents the control tone transmitted and illustrates graphically the action of the compressor shown in detail in Fig. 6. The line-906 .represents the time during which .the transmitting telegraph apparatus is disabled. I It will 'benoted that this time extends somewhat from line M3 to the time represented by the-verticalline 9M and this represents the hang-overperlodgprovided by the transmitting chain; 219. Line 901 is a composite picture of the linesignal showing first, telegraph tone signals and the n, after. the

line 908 represents the received signal at the distant end. Here the line signal of line 901 is efiected by fading and noise and hence has a considerably different appearance from that shown in the line 907 above. It will also be noted that this signal is displaced somewhat in time from the transmitted signal of line 901. In line 909 is shown the received telegraph signals after the telegrad has reshaped and retimed them and here the displacement in time is pronounced.

Line 9l0 represents the receiving telegraph checking circuit as controlled by the relay 339. Here the checking circuit does not operate for a time represented by the difference between the vertical line 9l5 and the vertical line 9|B which represents the hang-over provided by the condenser 349. Line 9 represents the received speech to the subscriber showing the action of the variable suppressor 234 in gradually opening and closing the speech path.

What is claimed is:

1. In a telegraph system, a transmission channel, means for transmitting telegraph signals in the form of alternating current over said channel, a telegrad for converting said signals into equal length direct current signals, said converted signals being displaced in time relation with respect to said alternating current signals, relay means for signaling the starting and stopping of telegraph transmission over said channel and a hangover circuit for said relay means for displacing the timerelation of said stopping si'g nal to correspond with the=displacedtime relation of saidv telegraph signals iins'aid telegrad;

2. In a communication'system; a transmissionchannel, means for normally transmitting. telegraph signals overzsaid channeLrvoicev controlled meansatithe transmitting end of said channel for stopping and starting .the said transmissioniof. telegraph signals over .saidtchannel, telegraph: receiving apparatus at'the' receivingend of said,

channel including atelegr'aph for converting .in-

coming telegraph signalsiintoa different form;-

the telegraph signals-outgoing. from said, .telegrad being delayed-in time relation with-respect.v to the corresponding telegraph signals incoming;

to said'telegrad, said' telegraph receiving apparatus including relay means; responsive to said voice controlled means-for-signaling to other telegraph'apparatus beyondsaid telegrad the start-- ing and stopping'of' the transmission. of. telegraph signals into said telegrad'and means for delaying the stopping signals by said relay-means for a period corresponding tothe delay of saidv telegraph signals whilep'assingthrough said telesgrad.

sion in said telegraph signal transmission "over said channel, said voicetcontrolledmeans inclird-" ing .direct controlled switching means :at: the

transmitting end and remote'icontro'lledswitche.

ing means: at the receiving end of saidichan'nel,

and means responsive to said remote controlled switching means for rendering telegraphreceiv ing apparatus beyond saidsignal .delaying means operative and inoperative, said last means being provided with hang-over means for delaying its said function of rendering said receiving apparatus inoperative for a period corresponding to the said delay in said telegraph signals.

4. In a communication system, a transmission channel, means for normally transmitting telegraph signals over said channel, means for alternativelytransmitting voice currents over said channel, switching means for changing to and from said normal condition from and to said alternative condition, voice controlled means for operating said switching means at the transmitting end of said channel and for connecting a source of control tone to said channel, means at the receiving end of said channel responsive to control tone for operating said switching means thereat, a telegrad in the path of telegraph signals at the receiving end of said channel, the telegraph signals outgoing from said telegrad being delayed in time relation to the corresponding signals incoming to said telegrad, a relay included in said switching means at the receiving end of said channel for controlling telegraph apparatus operated by the output signals from said telegrad, and means for delaying the release of said relay for a period corresponding to the delay to which said telegrad subjects the telegraph signals passing therethrough.

5. In a communication system, a teletypewriter printer, a selecting means in said printer operated by permutation code signals, a circuit including a telegrad for delivering permutation code signals to said selecting means, a printing relay in said printer for causing a printing oper- 3. In a communication system, a transmission: channel, means for normally transmitting telegraph signals over said channel,;voice'controlled1 'means for interpolating .voice current transmisf Lung" ation after/said 'selecting'means has .been completely set by said codesignals, saidltelegrad operatingto .displace .the. time relation between in-- coming and outgoing signals, .a .means for .controlling .said printingrelay operated from a vcir.-. cuit .associated.with the incoming terminals, of saidwtelegrad, and means for delaying thedisablingof said printing. relay for aperiodcorre-v sponding to the delay to which said telegrad subjects the. signals outgoing. therefrom.

6. ;In a system in which impulses comprising individual elements .of code combinations are received as groups of carrier waves the method of selectively .converting the groups of carrier waves to rectified code impulsesin a manner in which the code. .impulses aredelayed in time with respect to: the .corresponding groups of carrier waves ..and delaying ,byan approximately equal amountthe action ofucontrol pulses which are derived from received carrier. waves.

7. In a system of reception in .which control pulses .and signal .pulsesmarev selectively derived from received carrier Wavesbyapparatus which.

causes adisplacement of the signal pulses with respect to their corresponding carrier waves, thev condition,- the. means .for .translating. the code combination into intelligence having a delaying characteristic, in..combination..with means .for similarly. characteristically delaying the. conditioning. to1 a..non-translating condition. of the means for translatingthecode combinationsr 9. In a code. controlled tele-receiving system, means for receiving acode carrying wave and a Wave for suppressing fltele-receiving, means operative incidental to the receiving. of the..code

carrying Wave. for, delaying the effect of compo-,

nent parts thereof andlmeans operative to cor.-

respondingly delay theeffectof thewave for sup-.

pressing tele-receiving.

10. A receiving system comprising. detecting instrumentalities for detecting codedgroupsof waves to produce coded groups of imp.ulses,.a device. operated by the coded. group of. impulses .to make a record. in accordance .therewith, Vmeans incidental to said productiontovproduce .a time delay, detecting instrumentalities operatedby a control wave to .conditionsaid device .to a nonrecording .condition, .and .special means to delay production ;of the. non-recording. .condition by an amount equalto the time delay aforesaid whereby failure .to record properly a last. code impulse received. prior v.tothe reception of, the control wave. is prevented.

11. In .a receiving system whereinmeans operative .upon ,receptionoi a courier wave to inhibit telegraphic recording in preparation for speech reception, and wherein -meansoperative upon cessation of reception of the courier wave prepare forteleg'raphic recording, means for making the inhibiting means slow acting and the preparatory means fast acting.-

IRA COLE. ALFRED 'E M'ELHOSE, WALTER W. TU'II-IILL. 

